Electricity

• What are the two ways that a component can be connected in a circuit?

  Series and Parallel
• What are the characteristics of components connected in series and parallel?

  • Series: Total potential difference is shared between each component.
  • Parallel: Potential difference across each component is the same.
• What can be said about the combined total resistance of two resistors connected in parallel?

  The total resistance is less than the smallest of the two individual resistances.
• What can be said about the total resistance of two resistors connected in series?

  The total combined resistance is equal to the sum of the two individual resistances.
• How is the current described in a series circuit?

  The current is the same at all positions since the charge only has one path to flow through.
• How is the current described in a parallel circuit?

  The current is shared between the different branches, and it splits at junctions.
• How should an ammeter be connected in a circuit to measure current?

  Ammeters should be connected in series with the component they are measuring current through.
• How should a voltmeter be connected in a circuit to measure potential difference?

  Voltmeters should be connected in parallel to the component they are measuring the potential difference of.
• Why is it advantageous to connect lamps in parallel?

  If one lamp blows, the rest will be unaffected and can still receive current.
• What are the two equations for the power of a circuit?

  P = IV and P = I²R
• What are the units for power, current, potential difference, and resistance?

  Power (Watts), Current (Amperes), Potential Difference (Volts), Resistance (Ohms)
• What is the equation linking energy transferred, power, and time?

  E = Pt
• What are the units for energy, power, and time?

  Energy (Joules), Power (Watts), Time (Seconds)
• What is the equation linking energy transferred, charge flow, and potential difference?

  E = QV
• What are the two main factors that the amount of energy transferred by an appliance depends on?

  How long the appliance is used and the power of the appliance.
• Describe the energy transfers in a battery-powered torch.

  • Battery converts chemical energy into electrical energy.
  • Bulb converts electrical energy into light and waste energy (heating).
• Describe the energy transfers in a battery-powered motor.

  • Battery converts chemical energy into electrical energy.
  • Motor converts electrical energy into kinetic energy and waste energy (heating due to friction).
• What three things determine the power of a circuit device?

  The potential difference, the current, and the amount of energy transferred in a given time.
• What is the purpose of the National Grid?

  To link power stations to consumers for access to electricity.
• What are the two types of transformers used in the National Grid?

  Step-Up Transformers and Step-Down Transformers
• Where are step-up transformers found in the National Grid and what do they do?

  They are used when connecting power stations to transmission cables and increase the potential difference.
• Where are step-down transformers found in the National Grid and what do they do?

  They are used in connecting transmission cables to domestic buildings and decrease the potential difference.
• Why do transmission lines transfer electricity at high potentials?

  • High potential results in low current.
  • Lower current means less energy wasted as heat.
  • More efficient transmission of electricity.
• Why does the potential need to be decreased between transmission lines and houses?

  • Lower potentials are safer for domestic use.
  • Reduces the likelihood of severe electrocution.
  • Appliances are designed for 230V.
• Is mains electricity an a.c supply or a d.c supply?

  Mains electricity is an a.c supply.
• What do a.c and d.c stand for?

  1. c. stands for Alternating Current and d.c. stands for Direct Current.
• Define alternating current and direct current.

  • Alternating current: Current that continuously changes direction at a specific frequency.
  • Direct current: One directional current flow.
• What is the frequency and voltage of the UK mains electricity supply?

  Frequency: 50 Hz, Voltage: 230V
• How many wires are usually in the cables connecting electrical appliances to the mains? Name these wires.

  Three wires: Live wire, Neutral wire, Earth wire.
• What is the insulation colour used on the Earth wire?

  Green and Yellow Stripes
• What is the insulation colour used on the live wire?

  Brown
• What is the insulation colour used on the neutral wire?

  Blue
• What are the three wires usually found in cables connecting electrical appliances to the mains?

  Live wire, Neutral wire, Earth wire
• When does the Earth wire carry a current?

  When a fault occurs in the appliance, such as a surge or the casing becoming live
• What is the potential of the neutral wire?

  0 Volts
• What is the potential difference between the live and earth wires?

  230 Volts
• What is the purpose of the neutral wire?

  To complete the circuit by connecting the appliance back to the mains supply
• Where is the Earth wire connected in metal appliances, and why?

  The Earth wire is connected to the metal casing of the appliance to prevent electrocution if the live wire touches the casing
• What is the circuit symbol for a cell?

  + -
• What is the circuit symbol for a battery?

  + - + -